Both in the event the electromechanical machine is powered directly by direct current (e.g. brush motor) and in the event it is powered by alternating current via an inverter, the energy generated during braking phases of the machine is generally dissipated by a system connected to the DC bus. In most cases, this dissipation is done by resistors. When these resistors must store significant amounts of energy and/or when they must withstand a large number of operating cycles, they become heavy, bulky and expensive. Furthermore, the dissipation flow towards the wall of the housing in which they are fastened is, in these cases, difficult to control. This makes heat management of the application difficult.
FIG. 1 is an electrical diagram showing a traditional electric braking system with dissipation of the energy returned by the braking in a resistor. This electric brake system is arranged in the supply circuit of an electromechanical machine M. The supply circuit comprises a DC voltage source 1 supplying, via a protection diode Dp, an inverter 3 at the terminals of which the electromechanical machine M is connected. Between the cathode of the protection diode Dp and the −terminal the DC voltage source 1 is connected, inversely, a freewheeling diode Dl and a differential mode filter. The differential mode filter comprises an inductor L, wound around a magnetic circuit 2, and a capacitor C. The inverter 3 is connected to the terminals of the capacitor C. The electric brake system comprises a first branch comprising two diodes D2 and D3 connected in series and inversely to the terminals of the capacitor C. A second branch comprising a brake resistor Rf in series with a transistor (IGBT or other) referenced T is connected to the terminals of the capacitor C. The middle point between the brake resistor Rf and the transistor T is connected to the middle point located between the diodes D2 and D3. During braking of the electromechanical machine M, the braking energy is dissipated in the resistor Rf.
The operation of the circuit of FIG. 1 is as follows. When the electromechanical machine M supplies mechanical energy, the transistor T is controlled to be in the locked mode and no current flows in the resistor Rf. The diodes D2 and D3 are not operative in this phase. When the electromechanical machine receives mechanical energy, the inverter 3 returns electrical energy to the capacitor C. By making the transistor T conductive, usually via a PWM (Pulse Width Modulation), one then causes an electric current to pass in the resistor Rf and the dissipation in thermal form of the electrical energy returned by the electromechanical machine to the input of the inverter. The diodes D2 and D3 serve as freewheeling diodes for all of the parasitic inductors of the branch made up of the resistor Rf and the transistor T.
Document U.S. Pat. No. 6,072,291 discloses an electric brake system for an electromechanical machine connected to the output terminals of an inverter whereof the input terminals are supplied by a DC voltage source. The system comprises an electrical circuit connected between the input terminals of the inverter and comprising, connected in series:                a means for dissipating electrical energy returned by the electromechanical machine to the input terminals of the inverter during a braking phase of the electromechanical machine,        a switching means intended to close said electrical circuit during a braking phase of the electromechanical machine and to open said electrical circuit in the absence of a braking phase of the electromechanical machine.        
According to patent U.S. Pat. No. 6,072,291, the electrical energy, which is returned to the input terminals of the inverter during a braking phase, is primarily dissipated in a brake resistor.